The present invention relates to the field of automotive vehicle transmission devices, and more particularly relates to a manual transmission device providing a plurality of speed stages which is coupled to a hydraulically operated auxiliary transmission comprising a planetary gear mechanism and providing two speed stages.
A transmission device for an automotive vehicle such as an automobile, which is a combination of a main speed change device in the form of a conventional manually controlled gear transmission device which provides a plurality of forward speed stages and a reverse stage, and an auxiliary speed change device which provides two alternative transmission speed ratios, i.e. a low speed ratio and a high speed ratio, has already been proposed. Such an auxiliary speed change device is switched between its low speed stage and its high speed stage according to the overall general driving conditions in which the automotive vehicle is being operated, while on the other hand the main speed change device is switched between its various forward speed stages and its reverse stage in response to the moment by moment driving conditions in which the automotive vehicle is being operated.
For example, when the automotive vehicle is being operated in town traffic, or in a hilly area, the auxiliary speed change device is set to its low speed stage, and the main speed change device is used to provide the particular gearing ratio required, moment by moment, according to the speed of the vehicle and the acceleration required therefor. Thus, with the auxiliary speed change device in its aforesaid low speed stage, the transmission device provides a range of forward vehicle speed stages which provide, as a whole, relatively high reduction gear ratios, and which are therefore well suited for such city traffic driving, or driving in hilly country. Accordingly, in this mode of operation, because a more appropriate range of transmission gear ratios is available for these driving conditions, the performance and drivability of the vehicle are maximized, and the fuel consumption thereof is also made to be as high as practicable.
On the other hand, when the automotive vehicle is being used on the open road, such as upon an expressway, the auxiliary speed change device is set to its high speed stage. With the auxiliary speed device remaining set in its high speed stage, the manual operation of the main speed change device will provide a range of forward vehicle speed stages which provide, as a whole, relatively low reduction gear ratios. Thus, both the driving characteristics of the vehicle in high speed driving, and also the fuel consumption of the vehicle in such driving, are improved. Further, because a lower overall reduction gear ratio is provided for such high speed driving, engine vibration and engine noise are reduced during these conditions, because engine rotational speed is, as a whole, lower.
It has been previously practiced to shift such an auxiliary speed change device manually by the driver between its low and its high speed stages. With such a system of operation, the driver of the automotive vehicle must use his judgement as to whether he is currently operating the vehicle in the sort of driving conditions which merit the use of the high reduction gear ratio of the auxiliary speed control device, or of the low reduction gear ratio thereof.